The present invention relates to hydraulic piston axial pumps/motors of the type comprising pistons reciprocating within a rotatable cylinder block. Suction and discharge are both conducted via a common port plate, over which the pistons are revolved.
It has been for long recognized that these pumps suffer the inherent drawback of producing noise at such high db. levels that may cause damage to the human ear.
Several attempts have been made to solve this problem--cf U.S. Pat. No. 4,489,642 (Westveer--Dec. 25, 1984) and U.S. Pat. No 4,096,786 (Schauer--Jan. 29, 1978), both pointing at the solution in the direction of partly relieving the pressure shortly before the commence of the full discharge stage.
The object of the present invention is to improve the achievement of noise reduction along the line of the above concept.